Method of making a metallic filter



' June 2,1970

I INVENTOR. RICHARD J. LABOTZ ATTORNEY METHOD OF MAKING A METALLIC FILTER Richard J. La Botz, Fair Oaks, Calif., assignor to Aerojet-General Corporation, Azusa, Califl, a corporation of Ohio Filed Nov. 12, 1965, Ser. No. 507,315 Int. Cl. C23f 1/02 US. Cl. 1563 8 Claims ABSTRACT OF THE DISCLOSURE Ultra-thin metal members having accurately dimensioned fluid flow passages thereon and a method of making the same wherein a layer of etchant-resistant material is joined to at least one layer of etchant-susceptible material having a thickness equal to the desired depth of flow passages of the members, the layers of material forming a unitary structure. The etchant-susceptible material is masked to define a precise pattern of fiow passages thereon whereby when the masked unitary structure is exposed to an etchant bath and passages are etched to expose the etchant-resistant material, an ultra-thin metal member having a pattern of flow passages of precise dimensions is formed.

This invention relates to the manufacture of ultra-thin metal platelets, and has for its principal object the provision of such members having a precisely controlled pattern of elevated and depressed areas on at least one surface thereof.

While ultra-thin metal members having fluid flow passages on the surface thereof have heretofore been known, one of the major problems encountered in the manufacture of various articles of hardware utilizing such members, hereinafter sometimes called platelets, has been the production of accurate, uniform, smooth, photoetched flow passages. Accurate dimensioning of such passages is necessary in achieving desired characteristic of fluid flow through such passages, and thereby assuring achievement of desired operating characteristics of the article of hardware utilizing said platelets. With the use of conventional etching techniques, it is extremely difficult and costly to produce flow passages with the accuracy and degree of uniformity required. These difiiculties arise due to the fact that the depth of etch obtained at any location on the workpiece is a function of the etchant strengh, etchant temperature, etchant spray characteristics, and homogeneity and grain structure of the workpiece. Precise control of all these variables is required for uniform, accurate etching. To date, this required control has not been obtained. While alternate means of obtaining the precisely controlled pattern of elevated and depressed areas are available, such as selective plating or mechanical embossing, these too have their shortcomings.

In the present invention however, there is provided a method for obtaining accurate, reproducible-surfaced platelets wherein the depth and uniformity control of the etching of critical flow passages thereon is independent of the entire etching process. As will be hereinafter described, in the present invention the depth and uniformity are functions of the precision and uniformity of thin rolled sheet stock. Since it is well known that rolling can produce a highly uniform material, the present invention makes possible the production of etched flow passages on a platelet surface of a quality which is highly superior to that which can currently be produced with conventional etching or chemical milling techniques.

Other objects, aspects, features and advantages of the United States Patent invention will be apparent to those skilled in the art v Patented June 2, 1970 from the following more detailed description, taken in conjunction with the appended drawings wherein:

FIG. 1 is a partial section view of a layered article of manufacture wherein the two layers are of different materials; and

FIG. 2 is a partial section view of a layered article of manufacture wherein the top and bottom layers are of the same material, but are separated by a thin foil of braze material.

Referring now to the figures, there are shown articles of manufacture in the nature of platelets having on at least one surface thereof, a precisely controlled pattern of elevated and depressed areas which are utilized as fluid flow passages. In the present invention, the depth of etch control is not obtained by controlling the length of time the workpiece is in the etch bath, nor by the bath and spray strength, but rather by constructing the platelet to have a surface which is impervious to the etchant at the desired depth in the workpiece being etched. This is accomplished by using a sandwiched or layered construction, as shown in the figures, wherein two or more layers of material are metallurgically bonded together to form a single, integral sheet before being inserted in an etchant bath. Being well known to those skilled in the art, the details of construction and operation of etchant baths are not set forth in this application.

Referring now to FIG. 1, there is shown a partial section of an article of manufacture 10 which comprises an upper layer of one material 12, and a second material 14. The upper-layer material 12 is of the same thickness as the desired depth of etch and is subject to attack by the chemical etchant. The bottom layer 14 is bonded to the upper layer 12 and is selected so as to be inert to the etchant. When the composite sheet 10 is placed in the etching bath, the etchant removes all the unmasked portions of the upper layer of material 12, but etching stops when the etchant-resistant material 14 is reached. Thus, the depth and uniformity of the resulting etched flow passages are controlled only by the thickness and uniformity of the top layer 12.

A typical example of materials which might be used in such a process are nickel and 347 stainless steel. A cladding of nickel equal in thickness to the desired depth of etch is placed on the stainless steel. After masking, the sheet 10 is placed in a hot nitric acid solution which rapidly etches the unmasked portions of the nickel layer 12, but does not attack the stainless steel 14. After a suitable length of time, the piece 10 is removed from the bath with only the masked portion of the nickel layer 12 now remaining on the stainless steel 14. Layered materials of the type described are available commercially from a number of commercial sources including the Metals and Controls Division of Texas Instruments Incorporated. Layered materials may also be fabricated in a number of different ways. While the Texas Instruments material utilizes diffusion bonding, the materials might also be brazed together with an extremely thin foil or plating of braze material applied to one of the mating surfaces of the layers.

In the embodiment shown in FIG. 2, the upper layer 22a and the lower layer 22b are of the same material and they are bonded together with a foil of non-etching material 24. This thin layer of braze material 24 is utilized to control the depth of etch. Thus, the entire surface of the lower layer 22b is masked to withstand the etchant in the bath while the desired pattern is outlined on the surface layer 22a of the platelet 20 by masking.

Where accurate plating techniques are available, it is possible to plate the upper layer 12 upon the lower layer 14 of the washer 10 shown in FIG. 1. While it is contemplated that the layer 12 will generally be of rolled material, where it cannot be rolled to the precise thickness desired because of the strictness of tolerances imposed, the top layer 12 may be made slightly thicker than desired and the final adjustment in layer thickness made by subjecting the entire surface to the etching process. In that case, if, for example, the top layer 12 is ten percent too thick, subjecting this layer to an etch process giving a ten percent non-uniformity in depth of etch will result only in a one percent non-uniformity in the final etch.

It is to be understood that the forms of the invention herewith shown and described are to be taken as preferred examples of the same and that various changes in the shape, size and arrangement of the parts or steps of the process may be resorted to without departing from the spirit of the invention and of the scope of the appended claims.

What is claimed is: I. A method of manufacturing ultra-thin metal members having fluid flow passages of precise dimensions comprising:

joining a metal layer of thin etchant-susceptible material to a metal layer of etchant-resistant material to form a unitary structure, said etchant-susceptible material being selected to have the same thickness dimension as the depth dimension of the flow passages of the member being manufactured, said etchantsusceptible material having a uniform thickness;

masking the etchant-susceptible material in a precise predetermined pattern to define exposed areas of a desired width of the flow passages of the member being manufactured;

exposing the masked unitary structure to an etchant bath until said etchant bath has removed the unmasked portion of the etchant-susceptible material to a depth wherein the layer of etchant-resistant material is exposed; and

removing said unitary structure from said etchant bath.

2. A method of manufacturing ultra-thin metal members having fluid flow passages of precise dimensions comprising:

metallurgically bonding two thin layers of selectively etchant-susceptible, dissimilar metals to form a unitary structure, one of said metals being of uniform thickness having the same thickness dimension as the depth dimension of the flow passages of the member being manufactured;

masking said one metal in a precise, predetermined pattern to define exposed areas of a desired width of the flow passages of the member being manufactured; exposing the masked unitary structure to an etchant bath selected to chemically interact with only said one metal, said exposure continuing until said bath has removed the unmasked portion of said one metal to a depth wherein the other metal is exposed; and removing said unitary structure from said etchant bath.

3. A method of manufacturing ultra-thin metal members as described in claim 2 wherein a second thin layer of said one metal is metallurgically bonded to the other side of the other metal and the entire surface of said second layer of said one metal is masked prior to exposing the masked unitary structure to said etchant bath.

4. A method of manufacturing ultra-thin metal members having fluid flow passage of precise dimensions comprising:

joining a metal layer of etchant-resistant material between two metal layers of thin etchant-susceptible material to form a unitary structure, at least one of the layers of etchant-susceptible material being selected to have the same thickness dimensions as the depth dimension of the flow passages of the member being manufactured, each layer of etchant-susceptible material having a uniform thickness;

masking the one layer of etchant-susceptible material in a precise predetermined pattern to define exposed areas of a desired width of the flow passages of member being manufactured; masking the entire surface of the other layer of etchantsusceptible material; exposing the masked unitary structure to an etchant bath until said etchant bath has removed the unmasked portion of the etchant-susceptible material to a depth wherein the layer of etchant-resistant material is exposed; and removing said unitary structure from said etchant bath. 5. The method of manufacturing ultra-thin metal members having fluid flow passages of precise dimensions comprising:

joining at least one metal layer of etchant-susceptible material to a metal layer of etchant-resistant material to form a unitary structure, said etchant-susceptible material having uniform thickness and having not more than a 10% excess thickness greater than the depth dimenions of the flow passages of the member being manufactured; masking the etchant-susceptible material in a precise predetermined pattern to define exposed areas of desired width of the flow passages of the member being manufactured; exposing the masked unitary structure to an etchant bath until said etchant bath has removed the unmasked portion of the etchant-susceptible material to a depth wherein the layer of etchant-resistant material is exposed; removing said unitary structure from said etchant bath; removing the masking from the etchant-susceptible material; exposing the unmasked unitary structure to the etchant bath until said etchant bath has substantially removed the excess thickness of the etchant-susceptible material whereby the depth dimension of the flow passages of the member being manufactured is within 1% of precision; and removing the unitary structure from said etchant bath. 6. The method of manufacturing ultra-thin metal members having fluid flow passages of precise dimensions comprising:

joining at least one metal layer of etchant-susceptible material to a metal of etchant-resistant material to form a unitary structure, said etchant susceptible material having uniform thickness and having not more than a 10% excess thickness greater than the depth dimension of the flow passages of the member being manufactured; exposing said unitary structure to an etchant bath until said etchant bath has substantially removed the excess thickness of the etchant-susceptible material whereby the etchant-susceptible material will have a thickness within 1% precision of the depth dimension of the flow passages of the member being manufactured; removing the unitary structure from said etchant hath; masking the etchant-susceptible material in a precise predetermined pattern to define exposed areas of a desired width of the flow passages of the member being manufactured; exposing the masked unitary structure to the etchant bath until said etchant bath has removed the unmasked portion of the etchant-susceptible material to a depth wherein the layer of etchant-resistant material is exposed; and removing said unitary structure from said etchant bath. 7. The method of manufacturing ultra-thin metal mern bers having fluid flow passages of precise dimensions as defined in claims 1, 4, 5, or 6, wherein,

said etchant-susceptible material is nickel; said etchant-resistant material is stainless steel, and said etchant bath is a hot nitric acid solution. 8. A method of manufacturing ultra-thin metal memthe 6 bers having fluid flow passages of precise dimensions comacid etchant bath until said etchant bath has removed prising: the unmasked portion of the nickel to a depth Wherejoining a thin layer of nickel to at least one surface of in the layer of stainless steel is exposed; and

a layer of stainless steel to form a unitary structure, removing said unitary structure from said etchant bath. said layer of nickel being selected to have the same 5 thickness dimension as the depth dimension of the References Cit d flow passages of themembenbeing manufactured, said UNITED STATES PATENTS layer of nickel having a uniform thickness; masking the layer of nickel in a precise predetermined 3,364,018 1/ 1968 Kll'kpatrlck 75176 pattern to define unmasked areas of nickel having 0 width dimensions the same as the width dimensions 1 JACOB STEINBERG Pnmary Examlner gig: flow passages for the member being manufac- US. Cl. XR'

exposing the masked unitary structure to a hot nitric 156--18; 21'0506 

